Absolutely true, and again, related to the plague. The Iranian people are considered steppe people, although we might tend to picture them as desert-dwelling arab-types. They are quite different. The Sassanid Persians were fighting the Byzantines to a bit of a standstill (that was always the case) and at about that time, plague came in off the steppes and devastated the urban centers.
The Arabs came out of the desert full of Islam, and the Persians were in no shape to stop them, and the Byzantines were in no shape to stop them. The die was cast.
It is my understanding that Plague arrived from Egypt with rats on grain ships. You are right about the devastation though
Justinian was a great emperor but overreached trying to restore the western Roman Empire